1. Field of the Invention
The present invention relates to a method and apparatus for processing a substrate for use in the production of a semiconductor device (the method for processing a substrate will be hereinafter occasionally referred to as xe2x80x9csubstrate-processing methodxe2x80x9d and the apparatus for processing a substrate will be hereinafter occasionally referred to as xe2x80x9csubstrate-processing apparatusxe2x80x9d for simplification purpose). The present invention also relates to a film-forming method and a film-forming apparatus. The film-forming method includes a film-forming method for continuously forming a deposited film on a substrate by means of plasma chemical vapor deposition (hereinafter referred to as plasma CVD) or sputtering. The film-forming apparatus includes a film-forming apparatus for continuously forming a deposited film on a substrate by means of plasma CVD or sputtering. The present invention includes a process and apparatus for producing a photovoltaic element.
2. Related Background Art
In order to form a functional deposited film on a substrate using a plurality of processing chambers (film-forming chambers), there are known a number of apparatus for continuously forming a deposited film on a belt-like shaped substrate (that is, a web substrate) to obtain a semiconductor element. As a representative example of such apparatus, there can be mentioned a film-forming apparatus for continuously forming a deposited film on a web substrate by a so-called roll-to-roll system as disclosed, for instance, in U.S. Pat. No. 4,400,409 this film-forming apparatus comprises a double-chambered structure having a plurality of film-forming chambers: provided in a plurality of processing chambers communicated with each other. In said document, there is described that elements such as semiconductor elements having a semiconductor junction can be continuously formed by continuously transporting a long web substrate having a desired width in the longitudinal direction along a route of sequentially passing through the processing chambers. In the film-forming apparatus, each film-forming chamber is provided in the corresponding processing chamber whose inside can be maintained in a vacuumed state. In order to prevent processing gas used fox the formation of a deposited film in each film-forming chamber from being diffused or contaminated into the film-forming chamber situated next thereto, a gas gate is provided between each adjacent processing chambers. The gas gate comprises a slit-like separation passage through which adjacent processing chambers are communicated, where separation gas such as Ar gas, H2 gas or the like is flown into the separation passage to form a gas flow of the separation gas whereby the adjacent processing chambers are isolated one from the other. In each processing chamber, there are provided a means for introducing processing gas into the film-forming chamber provided therein, exhaust means including an exhaust pipe, a vacuum pump and the like for evacuating the inside of the film-forming chamber, means for performing plasma processing such as plasma CVD or sputtering by supplying a power energy such as high frequency power energy or the like to generate a plasma in the film-forming chamber, components of constituting the film-forming chamber, and a heating means such as a heater for heating the web substrate to a desired temperature for the film formation on the web substrate.
By using the plurality of processing chambers as above described, a plurality of deposited films each comprising a different material or having a different chemical composition can be continuously stacked on a substrate. However, as examples of the constitution of the apparatus such plural processing chambers there are considered (1) a case wherein one film-forming chamber is provided in one-processing chamber where one kind deposited film is formed on the web substrate in one processing chamber, (2) a case wherein a plurality of film-forming chambers are provided in one processing chamber where a plurality of deposited films of the same kind or similar kinds are sequentially formed on the web substrate in one processing chamber, and (3) a case wherein one of the plural processing chambers is used for heating, cooling or etching the web substrate without forming any deposited film thereon. For instance, Japanese Unexamined Patent Publication No. 191120/1997 discloses a process for producing a pin junction type photovoltaic element having improved characteristics wherein the p-type semiconductor layer is formed using a plurality of film-forming chambers which are different from each other with respect to certain condition. Particularly, in this document, there is described that using a film-forming apparatus comprising a plurality of processing chambers each having a film-forming chamber, a multi-layered semiconductor layer as the p-type semiconductor layer is formed by forming a desired deposited film in each of the film-forming chambers each provided in one of the processing chambers. It can be said that this apparatus constitution corresponds the above described case (1). Separately; in the above document, since the same processing gases (film-forming raw material gases) are in said each of the film-forming chambers for the formation of the p-type semiconductor layer, it is considered that the apparatus may take such constitution as described in the above case 2 in that all the film-forming chambers for the formation of the p-type semiconductor layer are arranged in one processing chamber.
Besides, in the case where the film formation in one film-forming chamber is difficult to achieve a desired film thickness, the desired film thickness can be achieved by arranging a plurality of film-forming chambers whose film-forming conditions are the same in one processing chamber as in the above case (2) and sequentially forming a deposited film by said plurality of film-forming chambers. Further, in the above case (2), it is possible to diminish the number of the processing chambers and that of the gas gates and therefore, the apparatus can be simplified and the cost of the apparatus can be diminished.
Incidentally, for the film-forming method by means of such roll-to-roll film-forming apparatus comprising a plurality of processing chambers communicated with each other as above described, it is suitable for mass-producing a functional deposited film or a semiconductor device such as a photovoltaic element or the like. However, particularly in order to widely spread the use of photovoltaic elements (solar cells) there is an increased demand for more improving the conventional film-forming apparatus and method so that they can stably and efficiently mass-produce a high quality photovoltaic element (solar cell) having a more improved photoelectric conversion efficiency, characteristic stability and characteristic uniformity at a reasonable production cost
As one of the important factors for the conventional film-forming apparatus and method to be difficult to comply with this demand, there can be mentioned a subject that the processing chamber or the film-forming chamber has such problems as will be described below with respect to the film-forming conditions relating to the control of the exhaustion and inner pressure of said chamber.
That is, in order to control the inner pressure of the film-forming chamber by evacuating (exhausting) the inside of the film-forming chamber, there is known a method of comparing an inner pressure value measured in the processing chamber or the film-forming chamber with a predetermined objective inner pressure value using a pressure controller and regulating the opening extent of a variable valve so that they are matched. Each of FIGS. 3 and 4 shows a substrate-processing apparatus in which said method for controlling the inner pressure of the film-forming chamber (the method will be hereinafter referred to as xe2x80x9cinner pressure-controlling methodxe2x80x9d) is used.
In the case of the apparatus shown in FIG. 3, there is a problem such that the pumping speeds for gases. exhausted from the respective film-forming chambers are not balanced but varied. In the case of the apparatus shown in FIG. 4, there is a problem such that the film-forming conditions cannot be readily changed.
This situation will be described in more detail in the following.
In the case of the apparatus shown in FIG. 3, variable valves 109a-109c are connected to exhaust pipes 108a-108c of processing spaces 104a-104c (film-forming spaces) in a processing chamber 103. For instance, measured values by pressure gages 106a-106c are inputted in pressure controllers 110a-110c having a valve-controlling function to control the opening extent extents of the variable valves 109a-109c whereby the inner pressures of the film-forming spaces 104a-104c are controlled, where feedback control is independently performed for each film-forming space. For the inner pressure-controlling method adopted in the apparatus shown in FIG. 3, there is a problem such that when the opening extent extents of the variable valves 109a to 109c are varied, the pumping speeds for gases exhausted from the respective film-forming spaces are not balanced but varied accordingly.
For the reason why such problem is occurred, it is considered such that as the respective film-forming spaces are provided in the same processing chamber they are conceivable to be spatially communicated with each other and because of this, due such factors as will be described below, a difference is occurred between the actual inner pressure of the film-forming space and the pressure which is recognized by the pressure controller.
As said factors, there can be mentioned (i) a variation in the error range for the zero point or linearity of the pressure gage, (ii) a variation in the error range for the set pressure value of the pressure controller or in said set pressure value, (iii) a variation in the set pressure value due to an output drift or a temperature change of the pressure gage itself during the film-forming treatment over a long period of time, (iv) a change in the reaction state of the processing gas in the discharge space (the film-forming space) due to abnormal discharge or discharge discontinuation therein, (v) a change in the closed state of the discharge space due to mechanical vibration of the substrate, and (vi) occurrence of electrical noise which influences to the inner pressure of the discharge space (the film-forming space). Because of these factors, the actual inner pressure of a given film-forming space is varied.
Specifically, for instance in the apparatus shown in FIG. 3, in the case where the set pressure value of the pressure controller 10c is varied due to any of the foregoing factors and the actual inner pressure of the film-forming space 104b is increased, the processing gas in the film-forming space 104b is flown into the adjacent film-forming spaces 104a and 104c to increase the inner pressure of each of the film-forming spaces 104a and 104c, where each of the pressure controllers 110a and 110c actuates to enlarge the opening extent of each of the variable valves 109a and 109c so as to decrease the inner pressure of each of the film-forming spaces 104a and 104c. In a state that the inner pressures of the film-forming spaces are varied in this way, when the opening extent and closing of the variable valves are serially performed, in extreme case, there will be an occasion such that the variable valve of a given film-forming space is entirely opened while the variable valves of the adjacent film-forming spaces are entirely opened.
And because the film-forming spaces are spatially communicated with each other as above described, in a worst case, although the inner pressure value in each film-forming space is maintained at a set pressure value, there is an occasion such that processing gas supplied into a given film-forming space is exhausted through the adjacent film-forming spaces, where the processing gas is contaminated into the adjacent film-forming spaces. And even when separation gas is flown into gas gates 101, similar phenomena are liable to occur.
The above problems due to such factors as above described are liable to occur also in the case where each of the film-forming spaces is provided in a different processing chamber and the film-forming spaces are communicated with each other through a gas gate (for instance, in the case of such positional relationship as shown in FIG. 4).
Description will be made of the inner pressure-controlling method in the apparatus shown in FIG. 4.
In the apparatus shown in FIG. 4, exhaust pipes 108a-108c of processing spaces 104a-104c (film-forming spaces) provided in processing chambers 103a-103c are gathered into a single exhaust pipe which is connected to an exhaust means, and a variable valve 109 is provided at the single exhaust pipe. The opening extent of the variable valve 109 is controlled by a pressure controller 110 on the basis of an output from any of pressure gages 106a-106c to control the inner pressures of the film-forming spaces 104a-104c, where the film-forming spaces 104a-104c are exhausted (evacuated) through the gathered single exhaust pipe. In this inner pressure-controlling method, by optimizing the pumping speed of the exhaust gas flowing in each of the exhaust pipes 108a-108c by means of an orifice or the like provided in each exhaust pipe, the inner pressure of each of the film-forming spaces 104a-104c can be made to be a desired pressure value. However, in the case where the film-forming condition is changed, specifically for instance, the flow rate of processing gas in a given film-forming space is changed, there is an occasion such that the inner pressures of the film-forming spaces 104a-104c are differed or the processing gas in one of the film-forming spaces is contaminated into the adjacent film-forming spaces to make it difficult to form a desired gas flow pathway and as a result, the film-forming conditions capable of being set are limited. This means that in order to change the film-forming conditions as desired, it is occasionally necessary to modify the constitution of the apparatus. Thus, there is a drawback for the inner pressure-controlling method used in the apparatus shown in FIG. 4 such that the film-forming conditions are difficult to be readily changed as desired.
The occurrence of such problems as above described is not limited only in the case of forming a deposited film on a web substrate. Similar problems are liable to occur also in the case where a web substrate is continuously transported to pass through a plurality of processing chambers while the web substrate being processed in each processing chamber. The processing of the web substrate in this case includes film-forming treatment by way of sputtering, vacuum evaporation or CVD other than plasma CVD, etching, thermal annealing and the like. The foregoing problems are more likely to occur particularly in the case where the gas composition and/or the inner pressure in one of the processing space are different from those in the adjacent processing spaces.
An principal object of the present invention is to eliminate the foregoing problems in the prior art and to provide an improved substrate-processing method and apparatus which enables to readily optimize the flow of processing gas in the processing space whereby making it possible to stably and continuously form a highly reliable deposited film having stable and uniform characteristics which are not deteriorated over a long period of time at a reasonable production cost. This situation enables to efficiently mass-produce a photovoltaic element (or a solar cell) excelling in characteristics at a reasonable production cost.
Another object of, the present invention is to provide a substrate-processing method comprising transporting a substrate to pass through a plurality of processing spaces communicated with each other while processing said substrate in each processing space, characterized in that based on an pressure of (a) one of said plurality of processing spaces, said inner pressure of said processing space (a) and an inner pressure of (b) at least one of the processing spaces arranged before or after said processing space (a) are controlled.
A further object of the present invention is to provide a substrate processing apparatus comprising a plurality of processing-spaces, a substrate transportation means for transporting a substrate to pass through said plurality of processing spaces while processing said substrate in each processing space, and a pressure gage of measuring an inner pressure of (a) one of said plurality of processing spaces, characterized in that said substrate-processing apparatus has a control unit for controlling the inner pressure of said processing space (a) and that of (b) at least one of the processing spaces arranged before or after said processing space (a) based on information obtained from said pressure gage.